The present invention relates to a lighting unit of display equipment which displays an image by adjusting the transmitted light intensity of the light, and in particular, to a lighting unit which uses a light source which has a plurality of different light emitting colors and display equipment provided therewith.
The display equipment is a medium which visually conveys the information to the human, and in the present day which has become a highly information society it is an important existence for the human and the society. The display equipment can be roughly classified in display equipment of emissive type such as CRT (Cathode Ray Tube), PDP (Plasma Display Panel) and the like, and display equipment of non-emissive type such as liquid crystal display equipment, ECD (Electrochromic Display), EPID (Electrophoretic Image Display), and the like.
The display equipment of non-emissive type is the one which displays the image by adjusting the transmitted (or reflection) light intensity of the light, and among these, in particular, the liquid crystal display equipment has recently been improved greatly in its performance and has been adopted greatly as display equipment for from the cellular phone to the personal computer, further for the large screen television and the like.
The liquid crystal display equipment is generally configured with a liquid crystal display panel which forms the image by controlling the transmitted light intensity or the reflection light intensity of the light and a lighting unit which is arranged on the rear of the liquid crystal display panel and illuminates the light to the liquid crystal display panel.
For the lighting unit there are an edge light type (a light-guiding member type), a direct type (a reflector type), and a planate light source type, and in particular, when realizing a lighting unit of thin type, the edge light type is used. The edge light type arranges the light source in the terminal part of the light-guiding member and conventionally the cold-cathode tube has mainly been used as a light source. However, recently, in the small size liquid crystal display equipment such as a cellular phone, the light emitting diode (LED) is used as a light source of the lighting unit. Further, LED which is a mercury-less light source has been adopted more and more also for the large size liquid crystal display equipment because it does not need an inverter which is necessary for the cold-cathode tube and from the point of view of the reduction of the environmental burden.
Also, when LED is used as a light source, when LED which emits the primary color lights such as red, green and blue is used as a light source, there is an advantage that it can realize display equipment which has high color purity and wide color gamut. In this way, when a plurality of LEDs which have different light emitting colors are used, in order to mix the lights of each color and make it an uniform white light, a color mixing area is provided in a part of the light-guiding member. As this color mixing area becomes an ineffective area from which the illumination light is not outputted, it becomes an obstacle to make the lighting unit small.
As a method to reduce this ineffective area, a lighting unit is described in Nicola et al., “New direction selective light extraction light pipe for LCD backlighting with LEDs”, Proc. IDW'02, p 505-508, 2002 or in JP-A-2006-4877, which in a lighting unit which has a wedge-type light-guiding member and a light source, among the facing surfaces which have different thickness of the light-guiding member, the light source is arranged on the terminal surface of the side of small thickness (thin) and a reflector is provided on the terminal surface of the side of large thickness (thick).
In this case, a plurality of light emitting colors are outputted from the different light sources and the lights which enter in the light-guiding member reach to the reflector without being outputted from the light-guiding member mixing the lights of each color. The light which is reflected at the reflector is light guided within the light-guiding member again, but this time it is reflected at the reverse side of the light-guiding member and is outputted to the obverse side. On this occasion, the lights outputted from the plurality of light sources are mixed and a uniform outputted light is obtained.
Namely, in the lighting unit described in Nicola et al., “New direction selective light extraction light pipe for LCD backlighting with LEDs”, Proc. IDW'02, p 505-508, 2002 or in JP-A-2006-4877, in the light-guiding member, an area where the lights of a plurality of different colors are mixed and an area to output the light are used for both purposes. Therefore, it is disclosed that a lighting unit which can obtain the light of uniform mixed color and has a small ineffective area can be realized.
In the lighting unit of edge light type, the thickness of the light-guiding member on the light source side is made to be thicker than that of the light source in order to improve the efficiency when the light outputted from the light source enters in the light-guiding member. Therefore, in the typical lighting unit of edge light type, the thickness of the light-guiding member becomes the thickest on the light source side.
On the other hand, in the above-mentioned background technique, there is a problem that the thickness of the light-guiding member becomes thicker than that of the light-guiding member used for the typical edge light type because it is necessary to make it thicker on the reflector side than on the light source side. Further, as the light source is to be arranged on one terminal surface of the light-guiding member, the number of the light sources which can be arranged is limited. For this reason, it has a problem that it is difficult to obtain a lighting unit which has the light intensity necessary for realizing light display equipment. These problems become notable in particular in a lighting unit for a large screen.